fix: address all Phase 1 code review feedback
All issues fixed:
- Issue 1 (Critical): Implement 7 behavior tests for AC6.1, AC6.2, AC6.3, AC6.7, AC6.8, and multi-identity variants using #[tokio::test], httpmock::MockServer, PdsClient::new_for_test
- Issue 2 (Critical): Fix clippy lint error on line 135 - replace &[device_key_uri.clone()] with std::slice::from_ref(&device_key_uri)
- Issue 3 (Critical): Fix 3 formatting violations (lines 72, 118, 128) with cargo fmt --all
- Issue 4 (Important): Add FCIS pattern classification comment on line 1
- Issue 5 (Important): Fix test_plc_monitor_creation - prefix unused monitor with underscore
- Issue 6 (Minor): Remove Step N: prefixes from comments in check_for_changes, keep descriptive parts only